These are all brass nickel plated "one touch" air fittings.      
Operating pressure 0-250 psi - vacuum rating 29" of mercury Hg.      
Operating temperature 0 F - 160 F      
All fittings are used - in New condition - with 90 day Warranty.      
Actual pictures of fittings.      
Part number starting with "P" have an integrated sealing ring.      
     Part #           Tube OD         Thread       Available    Price Ea.

P6520-08-06  1/2"        3/8" UNF     11      $4.00
P6520-05-06  5/16"(8mm)  3/8" UNF     15      $3.50
P6520-04-06  1/4"        3/8" UNF      1      $3.50
P6520-06-04  3/8"        1/4" UNF      3      $3.00
P6520-05-04  5/16"(8mm)  1/4" UNF      8      $3.00
 6520-05-04  5/16"(8mm)  1/4" UNF     15      $3.00
 6520-04-04  1/4"        1/4" UNF     25      $2.75
P6520-04-04  6mm         1/4" UNF      4      $2.75
 6520-53-04  5/32"(4mm)  1/4" UNF     22      $2.50
 6520-04-02  1/4"        1/8" UNF      0      $2.00
P6520-04-02  1/4"        1/8" UNF      5      $2.00
 6520-05-02  5/16"(8mm)  1/8" UNF      1      $2.00
 6520-53-02  5/32"(4mm)  1/8" UNF      4      $2.00
P6520-53-02  5/32"(4mm)  1/8" UNF      5      $2.00
 6521-53-32  5/32"(4mm)  10-32        34      $2.00
      
The following male connectors are available:      
P6510-08-08  1/2"        1/2" UNF      2      $2.00
P6510-06-08  3/8"        1/2" UNF      1      $2.00
P6510-08-06  1/2"        3/8" UNF      2      $2.00
P6510-06-06  3/8"        3/8" UNF      1      $1.75
P6510-05-06  5/16"(8mm)  3/8" UNF      8      $1.75
 6510-08-04  1/2"        1/4" UNF      2      $1.75
 6510-05-04  5/16"(8mm)  1/4" UNF      2      $1.50
P6510-05-04  5/16"(8mm)  1/4" UNF      4      $1.50
P6510-04-04  1/4"        1/4" UNF      0      $1.25
P6510-05-04  5/16"(8mm)  1/4" UNF      1      $1.25
P6510-53-04  5/32"(4mm)  1/4" UNF      1      $1.25
P6510-53-02  5/32"(4mm)  1/8" UNF      3      $1.25
 6510-53-02  5/32"(4mm)  1/8" UNF      3      $1.25
 6511-05-32  5/32"(4mm)  10-32         6      $1.25